Different types of centrifuges intended for processing blood and blood components and also several types of ring bags intended for use in these centrifuges are described in, for example, WO87/06857; U.S. Pat. No. 5,144,396; U.S. Pat. No. 5,732,050; WO97/30715; and WO98/35757. An apparatus for pooling buffy coat collections is described in U.S. Pat. No. 6,656,105. In the apparatus described in U.S. Pat. No. 6,656,105, the center well or central compartment or chamber to hold the platelet collection bag forms a cylindrical wall parallel to the axis of rotation of the centrifuge. This cylindrical wall provides a relatively large surface against which the platelets sediment under centrifugal force. This cylindrical wall also determines the sedimentation distance of the platelets.